While not necessarily so limited, the present invention is particularly applicable to heavy duty bulk conveyors of the type used to transport gravel, aggregate, coal and the like. Such conveyors can be of any length, and in some applications can extend several miles. The bulk conveyor is provided with a continuous belt which can travel at speeds of from about 300 to about 1100 feet per minute. Bulk conveyors of the type just described are well-known in the art. Generally, the bulk conveyor comprises a roller supporting framework having side members and appropriate transverse bracing. The roller supporting framework is, itself, normally supported at a convenient height by legs depending downwardly from the framework side members. Alternatively, the frameword could be suspended from an appropriate overhead structure. The upper flight of the continuous belt is supported at appropriate intervals by troughing roller assemblies so configured and arranged as to impart to the upper flight a transverse, trough-like cross section. The lower flight of the continuous belt is normally supported at appropriate intervals by single rollers extending transversely across the framework.
The present invention is directed to improved support for the return flight of the continuous conveyor belt. Prior art single, transverse, support rollers for the return flight are characterized by a number of problems. At times, problems are encountered with the belt not tracking properly, resulting in damage to the return rollers, the framework, and the belt. The relatively long return rollers are shaft mounted, and are subject to shaft deflection resulting in reduced bearing life. Finally, it has been found that the troughing rollers supporting the upper flight and imparting a trough-like cross section to the upper flight, actually tend to impart a shallow, trough-like, transverse "set" to the belt so that the lower flight is characterized by an inverted, shallow, trough-like transverse cross-section. As a result, the longitudinal edges of the belt tend to cut into the return rollers markedly shortening the roller life and damaging the belt edges.
The present invention is based upon the discovery that the above-noted problems in association with the return flight can be overcome by substituting for each single return roller an assembly of three shorter rollers arranged to define a supporting shape accommodating the shallow, inverted, trough-like set of the return flight. Guidance of the belt and tracking of the belt are markedly improved. Shaft deflection characteristic of long rolls is eliminated. Furthermore, in the new assembly, six bearings carry the same load as was carried by two bearings when the long single roll was used. Both of these advantages greatly lengthen the bearing life. Roll cutting by the conveyor belt longitudinal edges is eliminated. In some instances, the entire return roll assembly may be rotatively mounted at its vertical centerline for very limited pivotal movement, as will be described hereinafter. This slight pivotal movement will tend to cause the return flight to be self-centering.